Facebook is so valuable mainly because more than 850 million individuals use the product each month. Half that number come back every day.

In hindsight, something so massive and valuable as Facebook can seem almost historically inevitable.

But the truth is, Facebook's creation—and even its sustained development—was anything but a foregone conclusion.

We know this because back in college and in the year or so following, Mark Zuckerberg held lots of instant message conversations with friends and confidants about his plans for life and work. Due to a lawsuit or two, these instant messages were preserved. We have viewed some of them.

In one of these conversations, a 19-year-old Zuckerberg confers, during the fall of 2003, with his best friend from high school, Adam D'Angelo—who would become Facebook CTO and later cofound Quora—about which project he should focus on: a "dating site" he was asked to build for some Harvard seniors, or "the Facebook thing." Zuckerberg and D'Angelo discuss what "the Facebook thing" should be like.

Zuckerberg: So you know how I'm making that dating site

Zuckerberg: I wonder how similar that is to the Facebook thing

Zuckerberg: Because they're probably going to be released around the same time

Zuckerberg: Unless I fuck the dating site people over and quit on them right before I told them I'd have it done.

D'Angelo: haha

Zuckerberg: Like I don't think people would sign up for the facebook thing if they knew it was for dating

Zuckerberg: and I think people are skeptical about joining dating things too.

Zuckerberg: But the guy doing the dating thing is going to promote it pretty well.

Zuckerberg: I wonder what the ideal solution is.

Zuckerberg: I think the Facebook thing by itself would draw many people, unless it were released at the same time as the dating thing.

Zuckerberg: In which case both things would cancel each other out and nothing would win. Any ideas? Like is there a good way to consolidate the two.

D'Angelo: We could make it into a whole network like a friendster. haha. Stanford has something like that internally

Zuckerberg: Well I was thinking of doing that for the facebook. The only thing that's different about theirs is that you like request dates with people or connections with the facebook you don't do that via the system.

D'Angelo: Yeah

Zuckerberg: I also hate the fact that I'm doing it for other people haha. Like I hate working under other people. I feel like the right thing to do is finish the facebook and wait until the last day before I'm supposed to have their thing ready and then be like "look yours isn't as good as this so if you want to join mine you can…otherwise I can help you with yours later." Or do you think that's too dick?

D'Angelo: I think you should just ditch them

Zuckerberg: The thing is they have a programmer who could finish their thing and they have money to pour into advertising and stuff. Oh wait I have money too. My friend who wants to sponsor this is head of the investment society. Apparently insider trading isn't illegal in Brazil so he's rich lol.

D'Angelo: lol

There are two historically significant notes about this conversation:

It seems to be the moment when Zuckerberg decides not to work for somebody else, and to strike out on his own to build what would become Facebook.

It's D'Angelo, not Zuckerberg, who seems to suggest "We could make it into a whole network like a friendster."

In the months following his conversation with D'Angelo, Zuckerberg—along with a little bit of help from some Harvard friends, Eduardo Saverin and Dustin Moskovitz—built Facebook (then called TheFacebook), and watched it grow very popular very quickly.

By the next summer, Zuckerberg and pals moved to California and began working on Facebook full-time. By late July, Facebook had almost reached 1 million users, just 7 months after launching.

But despite that early success, a surprising instant message conversation between Mark Zuckerberg and a confidant on July 26, 2004—about who will foot legal bills in the event that Facebook were ever to be sued—reveals that Facebook was not his main priority at the time.

Confidant: Well you should recover the shares you need to recover legal fees.

Zuckerberg: I won't pay the legal fees

Zuckerberg: The company that buys us will haha

Confidant: Cool hopefully that'll be soon so you can move on and just work on what you want to

Even as a million people found themselves addicted to Facebook, Zuckerberg wasn't sure yet that it would end up being worth his time. To him, Facebook "just need[ed] to propel Wirehog," which has since been described as a file-sharing service.

How close Google came to owning Facebook—probably for a price approximately $99,990,000,000 lower than what Facebook will IPO for in just a few months.